Indoor Residual spray (IRS) in Malaria Control
1.
Vectors of Malaria
In India malaria is transmitted by nine vector species, six are of primary
importance. These are:
Anopheles culicifacies:
Transmits malaria in rural and
peri- urban
Anopheles fluviatilis
oothills
Anopheles stephensi
Areas in plains
In hills and f
In urban areas
Anopheles minimus
Anopheles dirus
In north eastern states
Anopheles sundaicus
In Andaman and Nicobar Islands
Anopheles annularis
Anopheles philippinensis
Anopheles varuna
Of these An.culicifacies is responsible for the transmission of 60-70% and
An.fluviatilis, 15-20% new cases of malaria in our country. Control of malaria in
India is actually control of An.culicifacies as each year 60—70% of the allotted
budget is spent for control of malaria in those areas where An.culicifacies is the
vector species for malaria transmission.
The understanding of the transmission of malaria is further complicated by
the existence of species complexes of cryptic species or sibling species or
isomorphic species in this team and also in other malaria vectors. Except for
An.stephensi all other malaria vector exist as species complexes comprising
several sibling species that result in considerable impact on the transmission of
malaria including susceptibility to commonly used insecticides in public health
programme.
2.
Vector Control:
Intervention measures to restrict the transmission of malaria by controlling
the vector population form the main part of the vector control. Effective vector
control strategies are based on four facts:
1
(i)
(ii)
(iii)
(iv)
Knowledge and understanding of vector biology
Surveillance of vector species
Incrimination of vector species
Public education and implementation of effective control
measures.
Vector control programme in India, as in the case with many anti-malaria
programme elsewhere, in the world, mostly rely on usage of natural and
synthetic chemical molecules, which have potential to kill the target insects.
Presently different formulations of synthetic chemical insecticides are in the
use for vector control. Wettable powder (WP) formulations are used for indoor
residual sprays while emulsion concentrate (EC) formulations are used for larval
control. For Indoor Residual spray (IRS) insecticides in use are DDT 50% WP,
malathion 25% WP and synthetic Pyrethroid (WP). Synthetic Pyrethroids include
deltamethrin 2.5% WP, Cyfluthrin 10% WP, lambdacyhalothrin 10% WP,
alphacypermethrin 5% WP, Etofenprox 10% WP and Bifenthrin 10% WP.
Synthetic pyrethroid insecticides are also used for impregnation of bed nets.
3.
Indoor Residual spray (IRS) : Most of the insecticides having residual
effect are sprayed indoors, so that mosquitoes after having bite on an infective
person will rest in the house and will pick up sufficient insecticide particles
sprayed on the walls and other indoor surfaces of the house and its longevity will
be reduced so much so that it does not survive to become infective. In areas
where the vectors are strongly endophilic, i.e. they tend to rest indoors, indoor
residual spraying of human dwellings can give very effective control. Vectors
that are exophillic i.e. they tend to rest outdoor but tend to feed or rest indoors
briefly, can be effectively controlled by indoor residual spraying with insecticides
that have good airborne effect. In areas where vectors are strongly exophilic
and/or exophagic, i.e. they rest and bite outdoors, other control methods, such as
use of insecticide treated mosquito nets or exterior space spraying (for
emergency control), should be considered.
In practice, the effectiveness of house spraying for malaria control
depends on adherence to the specified criteria of the insecticide and
application procedure, public acceptance of spraying, the availability of
well maintained equipment, adequately trained spraying personnel,
efficient supervision and strong financial support. The size of the area
depends on local circumstances and is influenced by the distribution of
malaria and malaria vectors; distance from important breeding sites, the
flight range of the vectors and demographic features:
3.1 Target area:
Generally, all the interior walls and ceilings are
treated. In addition to permanent human dwellings, field huts where
people sleep during the planting or harvesting season should be sprayed,
depending on local vector behaviour. The underside of furnitures, back of
the doors, outside caves and porch may need to be treated. It should be
noted that the residual effect of insecticides may be short on some
surfaces, e.g. porous mud walls, oil painted wood and alkaline white wash.
2
3.2 Selection of Insecticides: Several factors need to be considered in the
selection of an insecticide spraying, including availability, cost, residual
effectiveness, safety, vector susceptibility and excito -repellency. There
are large number of insecticides, which are used as aduliticides for indoor
residual spray. These are DDT, Malathion and different formulations of
synthetic pyrethroids.
The choice of insecticide for areas under the vectorial influence of
An.culicifacies:
This species is a vector for malaria all over India. It is a complex sibling
species– A,B,C, & D. All sibling species are efficient vectors of malaria
except sibling species “B”. A genetic variant of sibling species “B” transmits
malaria only in Rameswaram islands. Sibling species were found to differ in
their response to insecticides and also in the rate of development of
resistance to different insecticides. Based on these observations, the
following recommendations have been made in Malaria Action Programme
(MAP), 1995 for indoor residual spray:
Areas where species ‘A” is predominant:
Malathion 25% WP
Areas with species ‘B’ and ‘ C’
In most of the areas these
Species have already developed
resistance to malathion.
Pyrethroids use.
:
In areas where observations about sibling species ‘A’, ‘B’ and ‘C’ are
inconclusive, use DDT ensuring total coverage in Time and Space before
switching over to Malathion or Pyrethroids.
The other main vectors of malaria i.e., An.fluviatilis, An.minimus and An.dirus are
still susceptible to DDT. However, susceptibility status should be continuously
monitored and if the tests show development of resistance coupled with loss of
epidemiological impact of spray operations, the following strategy should be
adopted for change of insecticide.
Resistant to
Alternative insecticide
DDT
Malathion
DDT and Malathion
Synthetic Pyrethroids
3.3
Change of Insecticide:
If the change of insecticide is warranted, the state Govt. should support
their choice of alternative insecticide by documentation of data on vector
resistance studies and field observations on epidemiological impact of spray in
3
respect of insecticide in use. The change of insecticide will always be decided in
mutual consultation between State Programme Officer for NVBDCP, ROH&FW
and the Dte. Of NVBDCP with concurrences of State and Central Govts. The
proposal for any such change of insecticide should follow the following steps:
4.
(i)
State Govt. submits the proposal for change of insecticide to Dte.
Of NVBDCP in the month of January-February. All technical data
on vector resistance, epidemiological impact of the current
insecticide in use, along with financial outlay, quantity of alternative
insecticide chosen, with comparative cost difference for spray
operation should be included in the proposal. The proposal should
be discussed in the annual action plan meeting in Dte.of NVBDCP.
(ii)
Mutual consultations
between the State Progamme Officer
NVBDCP, ROH&FW and Dte. of NVBDCP in the month of MarchApril and report prepared in this regard for submission to Technical
Advisory Committee for approval under the chairpersonship of
DGHS, GOI.
(iii)
Approval of MOH&FW should be obtained in the month of AprilMay.
(iv)
Insecticide should be procured for next year’s spray operations and
fixing of delivery schedule should be ensured so that the insecticide
reaches the periphery by May-April next year i.e. well before
starting the first round of spray operation.
Insecticide formulations used under NVBDCP
The following formulations/compounds are used under the NVBDCP for
control of malaria:
4.1
DDT (Dichloro – diphenyl – trichloroethane):
In India DDT has been in use for malaria control since 1946. Recently
there has been a tendency to curb the use of DDT due to its persistence in
the environment. It is a fact that if DDT is applied in agriculture, it
contaminate water resources, enters the biochain and at each step of the
biochain, it gets more concentrated (bio-magnification) till it reaches
human beings. In human body, it is stored in the body fat and is excreted
in the milk. Therefore it reaches the infants right from the time of birth.
Since DDT persists for a long time in the community, there has been
apprehension that it will produce adverse impact on human metabolism
and growth. However, in spite of extensive use of DDT in agriculture, no
adverse reaction of DDT on human health has been reported so far.
A study group on WHO has recommended that at this stage there is no
justification on toxicological or epidemiological grounds for changing
current policy towards indoor spraying of DDT for vector-borne disease
4
control. DDT may therefore be used for vector control, provided that all
the following conditions are met.
a)
b)
c)
d)
It is used only for indoor spraying
It is effective
The material is manufactured to the specifications issued by WHO
The necessary safety precautions are taken in its use and disposal.
Govt. of India has constituted a mandate Committee on DDT which
reviews the use of DDT in public health and decides its quantity to be released
for the vector borne diseases control programme every year.
DDT has an added advantage. It is comparatively cheaper than the other
insecticides and even in those areas where resistance to DDT has been recoded
in studies with WHO test kits, the epidemiological impact of good spray
operations is seen because of its excito-repellent action.
Requirement of DDT:
150 MT per million population for two rounds of spray is required. In areas
where third round is proposed in selected villages, additional requirement of 75
MT per million population should be estimated.
4.2
Organophosphorous compounds: Malathion 25% WP is used under
the progamme in areas with DDT resistance. The disadvantage of
organophosphorous compounds is that unlike their use in agriculture where a
farmer uses the organophosphorous compound for crop protection only once or
twice a year, the spray squads engaged in spraying residual insecticide in the
human dwellings work with these compounds for periods extending up to 6 or 7
months. This long exposure results in acute toxic symptoms and if not controlled
properly may lead to mortality. Therefore, the spray staff engaged in spraying of
organophosphorous compounds are to be provided with more elaborate
protective garments and their blood cholinesterase level is to be checked
periodically to assess the toxic impact of the compound. These compounds are
also toxic to domestic pets.
Under Indian conditions, three rounds of spray with organophosphorous
compounds are given as against two rounds of spray with DDT.
In case of OP poisoning, the patient should be transported as soon
as possible to a doctor to receive an antidote. Organophosphate
poisoning, 2-4 mg of atropine should be given intravenously (for children
0.5 to 2 mg according to weight). Depending on symptoms, further doses
of 2 mg should be given every 15 minutes for 2-12 hours in severe cases.
Automatic injections are available for administration of atropine.
5
Requirement of Malathion25% WP:
900 MT per million population for three rounds of spray are required. If in
some areas a further round is required in selected villages, 300 MT per million
population for the special round for the population of selected villages only
4.3 Synthetic Pyrethoids:
These are new insecticides introduced for control of vector borne diseases in
India. The cost of these insecticides is much higher than the cost of DDT and
Malathion. Currently there are five insecticides of this group registered with
Central Insecticide Board for use in the programme.
These are (i)
Deltamethrin2.5% WP, (ii) Cyfluthrin 10% WP, (iii) Alphacypermethrin 5% WP (iv)
Lambdacyhalothrin 10% WP and (v) Bifenthrin 10 WP.
In treating pyrethroid poisoning vitamin E oil preparations can be given for
prolonged paraesthesia. Only in cases of definite allergic symptoms should
corticosteroids be administered. On occurrence of convulsions after sever
intoxication, intravenous injection of 5-10 mg Diazepam (or other benzdiazepine
derivatives) should be given.
Requirement of Synthetic Pyrethroids:
(i)
(ii)
(iii)
(iv)
(v)
Deltamethrin 2.5% WP: 60 MT per million population for two rounds of
spray. In some areas, where a further round is required in selected
villages, additional requirement of 30 MT per million for the population
of selected villages is estimated.
Cyfluthrin 10% WP: 18.75 MT per million population for two rounds of
spray and 9.38 MT per million population for selected villages which
would require special round/third round of spray.
Lambdacyhalothrin 10% WP: 18.75 MT per million population for two
rounds of spray and for a special round or IIIrd round of spray in
selected villages, 9.38 MT per million population may be estimated.
Alphacypermethrin 5% WP 37.5 MT per million population for two
rounds of spray.
Bifenthrin 10% WP : 18.75 MT per million population for two rounds of
spray and 9.38 MT per million population for selected villages which
would require special round/ third round of spray.
6
4.4 Insecticide formulations and dosages for IRSS.No.
Name of Insecticide
1.
2.
3.
Dosage per
sq.metre of
active
ingredient
Residual
effect in
weeks
DDT 50% wp
1 kg/10 Lit
Malathion 25% wp
2 kg/10 Lit
Deltamethrin
2.5% 400 gm/10 Lit
wp
1 gm
2 gm
20 mg
10-12
6-8
10-12
Area to be
covered by
10 lit.of
suspension
to get
correct
dosage
500 sq.m
250 sq.m
500 sq.m
4.
Cyfluthrin 10%wp
125 gm/10 Lit
25 mg
10-12
500 sq.m
5.
Lambdacyhalothrin
10% wp
Alphacypermethrin
5%wp
Bifenthrin 10% WP
125 gm/10 Lit
25 mg
10-12
500 sq.m
250gm/10 Lit.
25 mg
10-12
500 sq.m
125g/10 litre
25 mg.
10-12
500 sq.m.
6
7.
4.5
Preparation of
suspension in
water
Insecticide Resistance in Malaria vectors:
Presently insecticides belonging to different groups, namely,
organochlorine (DDT), organophosphate (Malathion), and synthetic pyrethroid
are used for public health spray. Insecticides belonging to the carbamate group
have yet not been introduced for public health sprays in India. Strategy for the
changes in the insecticides has always been reactive. Successive changes in
insecticide were made after the failure of the control by the ongoing insecticide
intervention. A subsequent change in the insecticides has lead to sequential
selection pressure of insecticides resulting in multiple insecticide resistant
malaria vectors. Malaria vectors in India are resistant to DDT alone or double
resistant to HCH or triple resistant to DDT, HCH, malathion and quadruple
resistant to DDT, HCH, malathion and Deltamethrin (synthetic pyrethroid). HCH
has been phased out of the programme in 1997. Of the six principal vector
species, two, namely An.culicifacies and An.stephensi have shown wide spread
resistance. Other vector species are mostly susceptible to these insecticides.
Development of resistance to synthetic pyrethroid warrants a caution of
impending possibility of wide spread resistance to other compounds of this group
that are introduced in public health programme for indoor residual spray as well
as insecticide treated bed nets.
7
4.6
Strategies of Delay/Avoid the onset of Resistance:
The most important aspect of the management of resistance is to either
avoid or delay. The onset of resistance by effectively manipulating or influencing
the factors responsible for the development of resistance. The methods include
avoidance of use of insecticide, that induce broad-spectrum resistance
mechanisms and confer cross resistance to chemically related and un-related
insecticides and sequential use of insecticides in rotation is preferred.
Possible ways of avoiding development of insecticide resistance in field






4.7
Avoid indiscriminate use of insecticides
Avoid use of insecticides that simultaneously select resistance to other
chemically related insecticides.
Avoid use of insecticides that induce development of more than one
type of resistance mechanism of broad spectrum of resistance.
Avoid use of the same insecticide both against adults and larvae.
Use of non chemical control methods, e.g. biopesticides, larvivorous
fish.
Use of synergist with insecticides to reduce physiological resistance.
Insecticide spray operations:
The indoor residual spray of human dwellings is as important for malaria
control in the community, as is the early case detection and prompt treatment for
an individual cure, therefore, it is essential that residual insecticidal spray should
be planned and implemented with sound technical skill under expert guidance. It
should not be entrusted to non-technical personnel like contractors,
voluntary bodies etc. In the revised approach to malaria control, it has been
decided to spray human dwellings and mixed dwellings. Cattle sheds are not to
be sprayed with a view to conserve insecticide, improve coverage of human
dwellings and the present diversion of mosquitoes from sprayed cattle sheds to
human dwellings.
4.8
Planning for spray operations:
The planning of spray operations will be done by the District Malaria Officer. He
involves the Medical Officer incharge of the PHCs in this process. The
epidemiological data should be thoroughly analyzed in this process. A meeting
of Medical Officer incharge PHCs should be convened by CMHO/DMO for this
purpose.
Under the MPO, the spray operations are to be carried out in all area with API 2
or above. However, the priority of spray will be given to High Risk areas all over
the country. Therefore, in “high risk” areas the population of ‘subcentre’
qualifying under the criteria laid down by the expert committee is considered.
The population is obtained from the epidemiological data collected from each of
8
the PHCs of the district. The Medical Officer incharge of PHC should bring this
information in the meeting at district HQ in the following format.
The District Malaria Officer should consolidate the information for the district in
the following format
PHC and sub-centres of “High risk” areas for spray operations
S.No.
Name of high
risk PHC
Population No. of high High risk
of PHC
risk subpopulation
centres in for spray
PHC
Remarks
In sub-centres with API 2 above (excluding the high risk sub-centres)
population of qualifying sub-centres only to be considered for spray in a PHC is
segregated in the following format :
S.No.
Name of the
PHC
Population
of PHC
Number of
sub-centres
having API 2
& above
Population of
sub-centres
having API 2 &
above qualified
for spray
Remarks
While planning for spray, the epidemiological data of preceding three
years are considered for selecting the population to be protected.
4.9
Spray Technique
The required quantity of insecticide should be issued to the squads each day by
the supervisor after checking balance stocks available from previous day’s
supplies. The insecticides used under the National Vector Borne Diseases
Control Programme (NVBDCP) are available as wettable powders.
The preparation of the spray suspension is made just before the start of the
spray operations every day. It is important that the suspension is made correctly
so that the correct dosage is applied on the sprayed surfaces. The procedure for
the preparation of the suspension is the same irrespective of the insecticide.
However, the quantity of the insecticide used per 10 litres of water will depend on
the insecticide used.
The required quantity of the insecticide is measured with a plastic mug and
poured into a 15 litre bucket. A paste is made with a small quantity of water.
The remainder of water is then poured slowly into the bucket and the insecticide
water mixture is stirred vigorously to obtain a uniform
suspension.
The
suspension is then poured into another bucket through a cloth sieve to remove
any particulate matter that might clog the nozzle of the spray pump.
9
The barrel of the stirrup pump is put in the bucket containing the spray
suspension. One man operates the pump and the other man sprays. The spray
lance should be kept 45 cms (18 inches) away from the wall surface. The swath
should be parallel. Spray is applied in vertical swath of 53 cm (21 inches) wide.
Successive swaths should overlap by 7.5 cm (3 inches). Spray is done from roof
to floor, using downward motion, to complete one swath; then stepping sideways
and spraying upwards from floor to roof. Do not let the spray drip to the floor.
Spraying is done on inner surfaces including eaves and roofs.
The discharge rate should be 740 to 850 ml per minute. To obtain the above
discharge rate, the pump man should give 20 to 26 strokes per minute with 10-15
cms plunger movement at a pressure of 10 PSI (0.7 kg/sq.cm) at the nozzle tip.
Spraying into a bucket for one minute and measuring the quantity of the
suspension in a graduated mug should check the correct discharge rate (740 to
850ml/minute). The nozzle tip should be discarded if the discharge rate exceeds
850 ml per minute.
If the spray stops due to a blockage in the nozzle, the nozzle cap be unscrewed
to remove the blockage and replaced with a new one. The blocked nozzle
should be put in a container with water for a few hours before the blockage is
removed with a finer wire.
A good quality spray should lead to uniform deposit on walls and other sprayable
surfaces. This is easy to verify for DDT and malathion sprays as the insecticide
deposits are clearly visible. Deposits of synthetic pyrethroids are visible on
wooden structures. The supervisor through physical verification should verify the
quality and coverage of spray randomly.
It takes about 5 minutes to spray a house with an average surface area of 150
sq. metres. A daily summary of spray operations should be maintained by the
field supervisor and verified by the health workers showing the areas covered,
percentage room coverage and insecticide consumption in the tables as below:
Villages Selected For Intervention Measures – Spray Operations
Spray Operations At Subcentre On ------------------------------Village
To be Sprayed
Sprayed
Houses
Rooms
Houses
Rooms
Locked/Refused
10
Daily Consumption Record Of Insecticide
Spray Operations At Subcentre
On_________________________________________________________
Insecticide Issued
(Qty.wp)
Balance
insecticide
available from
previous day
Number of buckets (5 litres)
Prepared
4.10
Consumed
SUPERVISION, PROCESS AND PERFORMANCE INDICATOR
Supervision of spray operations is a very important activity to ensure that spray
operations are carried out according to correct technical procedures, which is
essential for taking corrective action, and achieve the programme goals.
Supervision is carried at all levels of programme implementation. It can be
concurrent or consecutive.
A stratified sample should be taken up for
supervision.
Concurrent supervision
The following should be checked during such inspections:












Date of advance notification and the maintenance of time table for spray
operations
Turn out of spray crew
Nozzle tip discharge rate
Conditions of spray pumps
Preparation of insecticide suspension
Actual spraying operation including the technique, speed and coverage
etc.
Extent of refusal to accept spray and the numbers and percentage of
locked houses
Maintenance of spray records
Consumption of insecticide as determined by the quantity issued and
stock in hand
Date and time of checking of the squad by Inspectors/ Supervisors and
other supervisory personnel and their remarks, if any
Arrangements for mopping up
Future programme and time schedule
11
Consecutive supervision
The following is to be checked in consecutive supervision
 Evidence of insecticide deposit on sprayable surface particularly on the
ceiling and wooden material like windows etc.
 Dispersal of the insecticide deposits on the walls to verify uniformity of
deposits
 Number of rooms in each house sprayed satisfactorily, partially and not at
all
 Percentage of refusals and locked houses
 Factors responsible for not spraying any area as elicited through enquiries
from the residents
 Attempts made for mopping up operation in the event of high refusal
 Extent of mud plastering on the walls, if any and other relevant matters.
4.11
Community participation
Involvement of Panchayats in successful indoor residual insecticide spray
is an essential aspect of the programme. Panchayats/village/ local bodies/
village heads/ Block Development Officers/ Mahila Mandals, religious groups
etc., are to be informed about the spray schedule at least before a fortnight. This
advance information must be mopped up by Surveillance Workers/Malaria
Inspectors/ District Malaria Officer so as to facilitate the villagers to extend full
cooperation in getting actual spray inside of human dwelling with the objective of
full coverage of targeted population.
It is not the insecticide but the supervision and re-supervision of the spray
operations, which matter in the control of vector borne diseases. Ensure high
coverage of insecticide spray in terms of time & space.
12